One type of earth-boring bit has a body with at least one rotatable cone mounted to a depending bearing pin. Typically there are three cones, each having rows of cutting elements. The cutting elements may be machined from the metal of the cone, or they may comprise tungsten carbide inserts pressed into holes in the exterior of the cone.
The cone has a cavity that inserts over the bearing pin, forming a journal bearing. The clearances between the bearing surfaces are filled with a grease or lubricant. A seal assembly seals between the bearing pin and the cone near the mouth of the cone.
The seal assembly serves to prevent loss of lubricant to the exterior. Also, the seal assembly serves to exclude debris and cuttings of the borehole from entering the journal bearing. Typically the outer diameter of the seal assembly rotates with the cone and the inner diameter seals against the bearing pin in dynamic contact.
Many different seal assemblies have been proposed and used in the prior art. A variety of shapes of elastomeric seals have been employed. Elastomeric seals that have different materials on the inner and outer diameters are known. Elastomeric seals with carbon fiber fabric on the dynamic portions of the seal are also known. In addition, metal face seal assemblies including an elastomer that urges the metal faces together are also known.